None
Not Applicable
The invention is related to the field of data networks, and in particular to connection-oriented networks such as Asynchronous Transfer Mode (ATM) networks.
ATM networks support several different classes of service. Commonly known existing services include Unspecified Bit Rate (UBR) service, Available Bit Rate (ABR) service, Variable Bit Rate (VBR) service, and others. These different services are made available to network subscribers by equipment in the network, such as a collection of network switches along a path connecting subscribers for data transfer. A calling subscriber can signal which service type is desired by including a particular identifier in a call setup message that is sent along a path toward a called subscriber. The switches along the path examine the service identifier in order to establish certain operational parameters that will be associated with the connection, such as allocated bandwidth, relative priority, etc.
One distinction among services is whether a technique known as xe2x80x9cflow controlxe2x80x9d is employed in carrying out the service. When a flow control mechanism is in place on a network link, data cells are transferred from sender to receiver only when there is high assurance that a buffer is available for storing the packet at the receiver. In this manner, the chances of a cell being dropped at the receiver due to buffer overrun are reduced or eliminated. The sender is aware of this condition as a result of co-operating with the receiver according to the flow control protocol. Flow-controlled connections are generally more efficient than non-flow-controlled connections, because transmission bandwidth is not wasted sending incomplete frames of data, where a frame is a data unit used in network communications that consists of a number of cells. Flow control also reduces any tendency of network to experience the condition of xe2x80x9ccongestion collapsexe2x80x9d, which is characterized by persistent cell discarding and re-transmission such that little or no useful traffic is delivered.
Flow-control mechanisms are usually associated with a desired metric or goal for a given connection. For example, an ATM flow-control mechanism known as Quantum Flow Control or QFC is promulgated by an association of network equipment providers known as the Flow Control Consortium. The QFC protocol can be used, for example, to provide ABR cell service with essentially zero cell loss. ABR is characterized by bursty demand for network bandwidth. The QFC protocol provides a feedback mechanism from receiver to sender that enables the sender to control the cell transmission rate in accordance with the expectations for ABR service.
With the advent of flow-control protocols such as QFC in ATM networks, it has become desirable to map non-flow-controlled services to flow-controlled services, and vice-versa. Such mapping enables older xe2x80x9clegacyxe2x80x9d ATM devices to access devices that use the newer, more efficient services. The mapping is carried out in part during the call setup process. When a calling party requests a non-flow-controlled service such as UBR, the call can optionally be xe2x80x9cupgradedxe2x80x9d to a flow-controlled service. A switch or other network device through which the call is routed supports non-flow-controlled operation on the interface to the calling party, and supports flow-controlled operation on the interface on the route to the called party, for the duration of such an upgraded call.
Heretofore, the service request mapping functionality in a network device such as a switch has been controlled using a special-purpose workstation external to the switch. According to this scheme, a switch that receives a call setup message notifies the external workstation using a proprietary protocol. The workstation decides whether the call is eligible for upgrade based on interface configuration information. The workstation uses the proprietary protocol to notify the switch whether to upgrade the call or not. The workstation is responsible for processing all call setup requests, and controls all the switches through which call requests are routed. This technique has inferior scalability due to the reliance upon the external workstation. Also, the ability of the switch to operate in different types of network configurations is degraded, due to its reliance upon a non-standard protocol for controlling the service request mapping.
In accordance with the present invention, a technique for distributed control of service request mapping is disclosed that uses standard network management and signaling techniques rather than employing non-standard protocols and equipment. Scalability is improved, and network devices employing the distributed control technique can be used in a wider variety of network configurations by virtue of their enhanced interoperability.
A switch receiving a call setup request from a subscriber that specifies a non-flow-controlled service decides whether the call request should be upgraded to a flow-controlled service type. The decision is based on whether a boolean variable for the calling subscriber that appears in a management information base (MIB) is set to a value indicating that the subscriber is entitled to the upgrade. The upgrade is performed only if the variable is set to TRUE and the interface on which the call setup request is to be forwarded supports flow-controlled connections. When the switch decides to upgrade a call, the switch replaces the service type indicator in the setup message with a value indicating a flow-controlled service type, and forwards the setup message toward the called subscriber. If the MIB variable is set to a value indicating that the upgrade is not to be performed, it is still possible for a subscriber to request flow-controlled service directly, by indicating this service type in the original call setup message. Thus the service mapping technique provides a flexible way for subscribers to access higher-efficiency flow-controlled services.
In accordance with another aspect of the disclosed service mapping technique, a switch can decide to downgrade a call setup request under certain conditions. When a call setup message is received requesting flow-controlled service but destined for an interface that does not support flow-controlled operation, the switch replaces the service type indicator in the outgoing setup message with a value indicating a non-flow-controlled service type. The call downgrading functionality complements the call upgrading process by enabling network devices to maintain compatibility with subscriber terminals or other equipment that does not support flow control.
Other aspects, features, and advantages of the present invention are disclosed in the detailed description that follows.